Pep wary of Messi threat

Barcelona - Bayern Munich coach Pep Guardiola believes Lionel Messi is unstoppable on current form as he prepares to face his old club Barcelona for the first time in their Champions League semi-final, first-leg on Wednesday.

Messi and Guardiola won 14 trophies together during the latter's glorious four-year spell in charge between 2008 and 2012.

But the Spaniard insists even he doesn't have the formula to stop the four-time World Player of the Year, who has scored 51 goals in 50 games this season.